In ultrasonic nondestructive testing it is well known to inspect objects or workpieces by transmitting ultrasonic energy into the workpiece and receiving echoes of the energy reflected from the workpiece. In some forms of ultrasonic equipment, a cathode ray oscilloscope is utilized to display the echo signals or test information as a function of time. This permits the operator to observe the signals visually and to analyze and evaluate the significance of the signals. A considerable amount of the signal is of little, or no, interest to the operator; often a very small segment of the signal representing critical portions of the workpiece is of interest. Accordingly, it is customary to adjust the cathode ray tube so as to expand the display in time whereby only the portion or segment of the signal which is of interest is displayed. The expanded scale permits a more accurate observation and analysis of the test information.
When setting up the instrument, it has been very difficult to identify positively the particular portion of the test signal which is being effectively magnified by time-expansion and displayed to the operator. It has been possible to adjust the instrument so that the entire test signal is displayed or to adjust it so as to display a particular portion of interest. Frequently, it has been difficult to precisely correlate the two alternate displays, one with the other. This has necessitated a considerable amount of time and careful attention by the operator when setting up the instrument so as to be sure that he has effectively focused the instrument on that part of the test signal which is important. In many instances the test information is extremely complex in its content and this has led to some confusion. As a result, on occasion, the instrument has been focused on immaterial portions of the signal.